Various different methods are known for improving the capacity of existing optical networks. One method involves the use of so-called wavelength multiplexing technology (WDM) for improving the extent to which available bandwidths can be utilised on an optical fibre in the optical network. Wavelength can also be used in an optical network as an information address. This requires the use of different types of wavelength selective components. For instance, wavelength selective modulators (WSM) may be used to this end.
No methods or devices are at present available for the wavelength selective modulation of optical channels in cases when the channels lie relatively close to one another, which presents a problem.